Polycarbonate resins formed of 2,2-bis(4-hydroxyphenyl)propane (referred to as “BPA” or “bisphenol A” hereinunder) have been used in various optical material applications such as substrates of CD or DVD, optical films, optical sheets, a wide variety of lenses, or prisms since they are excellent in transparency, heat resistance, low water-absorption properties, chemical resistance, mechanical characteristics, and dimension stability.
However, the bisphenol resins formed of only BPA have a large photoelastic coefficient, and the molded articles formed of the resins may have large birefringence due to the relatively inferior melt-flowability thereof. And the resins have a high refractive index, 1.58, but they have a low Abbe's number, 30, which indicates that the refractive index and the Abbe's number are ill-balance. Therefore, they suffer from the disadvantage of not having capabilities sufficient for being used in a variety of the applications such as optical recording materials and optical lenses. Furthermore, they suffer from the disadvantages of having the low stainability and of forming only the lenses of the limited color
For solving the disadvantages of the BPA-polycarbonate resins, the copolymer of BPA and an aliphatic-compound such as tricyclo[5.2.1.02,6]decanedimethanol (referred to as “TCDDM” hereinunder) has been proposed (see Patent Documents 1-3). However, since the polycarbonate containing the aliphatic structure is slightly inferior in terms of the heat-resistance, compared with any aromatic polycarbonate, the tendency thereof is large, and therefore, it is especially difficult to obtain an aromatic-aliphatic copolymerization polycarbonate having a large molecular weight and an excellent hue.